Polymerization of maltose



May 14, 1946. G, L LEUCK 2,400,423

POLYMERIZMION 0F MALTosE Original Filed Feb. 9, l942` l palizas/e1 F3 .Meta 50?'0 czfo IN V EN TOR.

Patented May 14, 1946 POLYIVIERIZATION F MALTOSE Gerald John Leuck, Evanston, Ill., assignor to Corn Products Refining Company, New'York.' N. Y., a corporation of New Jersey original application February 9, 1942,'serial No.

Divided and this application August.

21, 1944, serial No. 550,382

1a claims. (c1. 26o-209) This invention relates to the polymerization of sugars, and more particularly to the polymerization of dextrose and maltose. The principal object of the invention is to provide n efficient and relatively inexpensive process for the production of a polymerized sugar product which will contain a large quantity of sugar polymers, in pro- ,portion to the amount of sugar treated, and in which the polymers will contain a large average number of dextrose units; that is to say, a product in which the amount vand also the degree of polymerization are high. This application is a division of application Serial N0. 430,162, filed trose involves the elimination of one molecule of water from the anhydrous dextrose treated, as well as the building up of the dextrose anhydride units into polymers of varying degrees of polymerization. It should be observed, howeventhat during the polymerizing operation the dextrose anhydride unit may undergo various transformations into CeHioOs configurations; and the term dextrose polymers" as used herein, is intended to cover all such configurations. It should also be remarked that the polymers produced in accordance with this invention need not consist of single CeHioOs molecules. They may consist of two or more such molecules combined as glycosides. By dextrose polymers is intended the product, whatever its chemical nature, which re- 40 sults from the polymerizing operation, including essential changes and other chemical reactions that may take place incidentally to the polymerizing operation including the alteration o f the dextrose anhydride configuration.

Another and very important object of the invention is to provide a polymerization process in which the formation of color will be reduced .'to a minimum.

I'he dextrose. used for the production of the beta anhydrous dextrose is in a relatively pure state. Most of the beta anhydrous dextrose of commerce contains a large proportion \of alpha anhydrous dextrose, and this mixture is not suitable for polymerization according to the present process, although it may be used and a. product polymerized to some extent produced thereby.

It is also possible to use hydrate dextrose, in a crystalline state, and obtain satisfactory results provided suitable operating methods are emp1oyed,`as hereinafter described.

It is also possible to use dehydrated dextrose crystals butthe results appear to be less satisfactory with respect to amount and degree of polymerization and color.

The process does not appear to be applicable. according to present experience, to sucrose or xylose; but can be ,used effectively for the polymerization of maltose, a disaccharide composed ofl two dextrose units. It is believed, for reasons to be stated, that the process can, in fact, be used for the polymerization of any reducing or dextrose polysaccharide, thatis any sugar which is composed of dextrose units.

A strikingly characteristic feature of applicants process is that' the sugar (which will be referred to hereinafter as dextrose with the understanding that the process is also applicable to polymerized product may be alpha anhydrous dextrose in a crystal state. Commercial alpha anhydrous dextrose, which is a high purity product, is suitable for the purpose. The dextrose should be in the form, preferably, of fairly large sized crystals, such as those of the usual commercial product averaging from 20 to 100 mesh per linear inch. It should not be pulverized.

It is also possible to use'beta anhydrous dexmaltose and other dextrose polysaccharides) is polymenzed without destroying or impairing the individuality of the dextrose crystals as to form. The crystals are not reduced to a molten state, although they may possibly undergo a slight, incipient melting or softening superiicially. 'By referring to the sugar as not being reduced, in or prior to the polymerizing operation, to a molten state, it is not intended to negative the possibility l of the crystals being superficially melted as just stated. The term molten state as used herein implies melting to the extent that crystal structure is substantially obliterated. The product, `the'refore--the polymerized dextrose-may be appropriately referred to as a product of "crystalinvention is the use, as catalysts, or as primaryv catalysts, of boron compounds, for example, borlc anhydride, and tetra, meta and ortho boric acids.

trose; but the process is not eflicient unless the o Theoretically, because the process is intended to While a boron compound (which hereafter forA convenience will be referred to as boric acid) appears to be essential, as a catalyst (at least for the polymerization of dextrosel--so that, because the process involves using this substance in relatively large quantities, it may be regarded as the primary catalyst in the dextrose polymerization reaction-by far the best results are obtained when a small amount (which in some cases may be a mere trace) of a secondary or co-catalyst is employed with boric acid. The secondary catalyst may be an acid, an'acid salt or a neutral salt. A llaline salts are excluded because of vtheir destructive effec't'brl' the dextrose. The secondary catalyst maybe-present as an impurity in either the dextrose or in the primary catalyst; or it may be present in the atmosphere, particularly acidic material such as sulphur dioxide for hydrOgen chloride; and in the specific examples which fol-. low the polymerizing operationswere carried out, unlessv otherwise specified, in the presence of traces ofthe secondary catalysts in the materials treated and in the atmosphere.A

It has been further discovered by applicant that these secondary catalysts, if used in appreciable quantities, lower the polymerizing temperature of the dextrose, so that the process may be carried out eiiiciently at relatively low temperatures. This is desirable in order to minimize color formation which is a function of temperature. Any acid or other acidic material or neutral salt, suitable for use as a co-catalyst with the boric acid, will reduce the polymerizing temperature.

The polymerization is brought about ordinarily by heating the dextrose at a temperature below the melting point of the dextrose, viz. 146 C.

Y (295 F.) However, with large quantities of boric acid in a finely divided state, it is possible to operate somewhat above the melting point of the dextrose for reasons to be stated.4

It has also been found that the amount and degree of polymerization can be increased, without bringing about melting of the material, if, after the dextrose has been subjected in the presence of the catalyst, to a temperature below or near its melting point, but at or above a tempera.-

ture which will bring about incipient polymerization, it is then subjected for a. time to a temperature very considerably above its melting point. In

`fact, this eiect may be obtained even if the first heat treatment, because of the low temperature employed, brings about little or no polymerization according to the analytical methods used for determining amount and degree of polymerization.

All of these procedures aim at obtaining polymerized products which will be as nearly white as possible, that is` which, as to color, will resemble as nearly as possible the crystalline dextrose treated; which will contain as large a quantity of polymers as possible, in proportion to the resulting from the polymerization process may- `be carried on so far as possible under anhydrous conditions, boric anhydride is to be preferred possible, that is, will contain, on the average, as large a number of dextrose units as possible.

However, it is realized that for certain purposes all of these characteristics may not be essential. For example, polymeriz'ed dextrose product having a low polymer content and a relatively low degree of polymerization may be useful for cer tain purposes. In all cases coloration is to be avoided as far as possible.

The product may be used advantageously as a 'humectant, for example, as a substitute for glycerin in the treatment of tobacco. The invention is in no way limited to this particular use. The dextrose polymers of this invention are characterized by low reducing values in comparison with other reducing poly-saccharides such as the disaccharide maltose or the trisaecharide raiiinose. For example low degree polymers of this invention which average two or three dextrose units appear to have reducing values considerably less than maltose and raiiinose respectively.

The products of 'this invention are heterogeneous mixtures of polymers having a wide variation in degree of polymerization. h'While the dextrose polymer-boric acid mixture have utility for certain purposes, it has been realized that, generally speaking, it will be necessary to remove the catalyst from the dextrose polymer product; and one of the objects of the invention has been to provide a process for effecting such removal of the catalystthe boric acidamount'of the sugar treated; and in which the and the recovery of the same for re-use, as well as the recovery for re-use of the agent (methanol) used for effecting the separation of the boric acid from the dextrose polymer product.

The removal and recovery process is illustrated in the accompanying flow sheet drawing.

The processes outlined .above are exemplified in the following specific examples of the reduction to practice of the invention. It will be understood, however, that these examples are purely illustrative and typical. The invention is not to be regarded as limited to the particular operating data given therein.

Before description of the speciilcexamples, it

will be necessary to describe the analytical method used for determining the amounts and degrees of polymerization referred to, for purposes of comparison, in the specific examples. It will be understood that the pclymerized product is subjected to analysis, in all cases, after the boric acid has been removed from the product.

Method of determining amount and degree of 'polymerization A 13.3% solution is made by adding distilled water to the dextrose polymer. 15 cc. of this water polymer solution, in which the dry substance is equivalent to 2 grams of the original dextrose, is used for making the tests. To this 15 cc. polymer solution there is added, in three stages, anhydrous isopropyl alcohol, and the precipitates are removed after each addition of the alcohol. At the rst stage 20 cc. of alcohol is added to the 15 cc. polymer water solution. At the second stage 15 cc. of alcohol is added so that the alcohol content of the solution at this stage is 35 cc. At the third stage 50 cc. of alcohol is added so that the alcohol content of the solution is 85 cc. The precipitated substances, at all stages, are dextrose polymers but of diil'erent degrees, on the average, of polymerization. 'I'he isopropyl alcohol test is based on the fact that pure dextrose itself is completely soluble in aqueous isopropyl alcohol as well as in water.'y whereas dextrose polymers, which are soluble in water, are insoluble in aqueous isopropyl alcohol and this insolubility depends (l) upon the alcohol content of Y v the solution, the more concentratedthe sblution the greater the insolubility of the dextrose polyj nier; andv (2) upon the degree of polymerization of 'the' dextrosepolymer, namely, the higher the degree of polymerization, that is, the greater vthe number of dextrose units in the dextrose polymer,

thegreater.) the ,insolubility of the polymer in a wate oiio'pylalcohol solution of a given alcohol' co `entration. If no precipitate is obtained in thef85fcc`. aqueous isopropyl alcohol solution .the assumption is that no polymerization has taken.,place and the dextrose is still all there in .its original form; cr possibly, that the material consistsl mostly of dextrose but with a small amount of dextrose polymer; or, it may be, that the material consists entirely of polymer products but of a low degree of polymerization. In..

any case, there is no substantial formation of ent probably through surface adsorption. The removal o1' this water, :if not essential, is preferable. 'Ihere-is added to andl blended with the dextrose5%. by Weight, of iinely powdered meta boric acid. The meta boric acid is also preferably, pre-dried and should be powdered fine enough to pass through a 170 mesh screen (170 meshes to the linearinch) or, which is preferable, so as to pass through a 200 mesh screen. AIn

fact, the nner the boric acid is powdered, the better are the results obtained. This blended mixture is then spread out in a thin layer and heated to a temperature of 135 C. (275 F.) at

l which temperature it is maintained for 5 hours.

When the 15 cc. polymer solution is treated with isopropyl alcohol, the polymer is precipitated in the form of an emulsion or very ne dispersion which ordinarily cannotv be ltered but is .best centrifuged. Each centrifuging operation gives a light upper layer of isopropyl alcohol containing dextrose and such dextrose polymer as does .not precipitate at the particular alcohol concentration, and ay heavy lower layer of the precipitated dextrose polymer. The heavy or lower layer is evaporated to constant weight and the ratio of this to the total dry substance weight of the specimen treated represents the per cent precipitated at this particularstag'e.

The degree o f polymerization, at each stage, is made by a recognized molecular weight determination such as by determining the extent towhich the freezing pointof a 10% or 20% aqueous solution of these polymers is lowered. By ascertaining the molecular weight of the polymer one can compute the number of dextrose units in the polymerv since it is known that a dextrose ypolymer consists of dextrose units wherein two or more Alpha anhydrous dextrose in a crystalline state is dried at 80 C. (176 F.) for twelve hours in order .to remove anywater, free or molecular, that the material may contain'. This example assumes the use of commercial crystalline alpha anhydrous dextrose, which will ordinarily con-v of polymers havingmolecular weights ranging The product is a granular material of crystallike character, as that `term is defined above, in which the individuality of the original dextrose crystals as to their form has not been lost. That is, the process of polymerization has transformed the dextrose crystals, separately and individually,

into granular particles, containing or consisting v of dextrose polymers, without substantially affecting the contour and shape of original dextrose crystals. The product in color is only slightlyv "darker than the original dextrose crystals.

I n this example, other conditions being as stat'- ed, a possible range of temperatures will be between about 133 C. (271 F.) and 145 C. (293 R); and the lower the temperature .within this range, the greater the amount and degree of polymerization.

The isopropyl alcohol-analysis of the product in accordance with the method specied above is as follows:

Table 1 tg Degree of isopropyl alcohol added to 15` cc. DOlYmel tollbilggnzgd polymer solution to give alcohol precipitated bv number contents of- "n total dry o'f dextrose substance it in Sample lill S The figures under Degree of polymerization, etc. represent a mathematical average which may cover a wide range of molecular weights.,

Qualitative tests have indicated that small fractions of the portion of polymerized product precipitated with the iirst addition of 20 cc. isopropyl alcohol represent dextrose polymers containing as high as forty to fifty dextrose units. This, in turn,` would imply the presence in the sample between 6480 and 8100. Since the molecular weights of high lsoluble dextrines range between about 10,000 and 20,000, it can be said that the dextrosepolymers formed in accordance with this invention begin to approach the degree of polymerization of modified starch products.

Polymerization theories Several theories may be advanced to explain why it is possible to polymerize dextrose crystals without reducing the dextrose to a molten state;

ment of crystalline dextrose is of such a nature as y to give the .boric acid an opportunity of reacting tain asmallfractlon (about 0.25%) of water pres-l with some of the hydroxyl (OH) groups oi! the such that the boric acid does not have the op-r portunity to react with hydroxyl groups, in a manner similar to that taking place with dextrose. From the above theory it may be assumed, that any crystalline sugar which has a space lattice wherein hydroxyl groups are capable of reaction with boric acid in a manner similar to that of boric acid and crystalline dextrose should4 be capable of forming sugar polymers in the presence of boric acid catalysts Without destroying.

the crystal-like form of the sugar. The theory is consistent with applicants discovery that the process described for dextrose will work in the case of maltose which consists of two dextrose Another theory is that as the dextrose crystals are heated. they are softened or melted slightly at their outer surfaces but not enough to aiect substantially the shape of the crystals. These melted or softened surfaces are coated with 'the line boric acid powder particles. The boric acid dissolves into and thenpolymerizes this surface dextrose as fast as the melting occurs.` The dextrose polymer being infusible forms a protective coating which prevents the, crystal from melting, except initially and superlcially, and thereby preserves the form of the original crystal. Theboric acid, on the other hand, continues to diifuse into the crystal interior, because of `the softened condition. The boric acid` powder also serves as a. surface-active agent which keeps the individual dextrose crystals from fusing together during the initial superficial melting. The statement in the claims that crystals are not reduced to a molten state is not intended to exclude a superficial melting or softening of the crystals.

It is quite possible that both of these theories are correct.

Under the conditions of Example No. 1 the As thel polymerization of the dextrose involves the splitting off of water from the dextrose (the opposite of the hydrolysis which occurs when a rdextrose polymer, e. g. starch, is converted to merization is that which is at the points of conrange of polymerizing temperatures has to be i narrow, if the process is to be eiilcient. The range is approximately between 133 C. (271 F.) and 145 C. (293 FJ. Below 133 C. the dextrose does not polymerize to any substantial extent. Above 145 C. the dextrose will melt before becoming polymerized. However, as will .be shown in examples which follow, after partial polymerization, or even after heat treatment below the normal polymerizing temperature, the material may be heated at temperatures very much above the melting point of dextrose, without melting the crystals, with an increase of the amount and degree of polymerization and without undesirable color formation. s

The heating (referring to the Example No. l and'v those to be described hereinafterymay be done in an ovenvwith the material spread out in trays or in a rotary drum heater or in any other way whereby there will .be a4 uniform distribution of the heat.

" cules of water.

should be the best catalyst; and this is the fact;

tact with crystal surfaces of the dextrose. 'I'he smaller the particle size of the boric acid, the greater will be the amount of boric acid, in the total amount actually used, which will be in contact with the dextrose crystal surfaces and therefore effective to produce polymerization. One might, for example, use 35% of boric acid of 20 mesh pulverization and obtain less polymerization than with 1% of 200 mesh boric acid. The boric acid may be ground mechanically and blended with the crystalline dextrose by means of a suitable mixing apparatus. Or the dextrose crystals may be suspended in a liquid solvent of boric acid such as acetone, in which dextrose is insoluble, and the solution-suspension evaporated '4 tocoat the dextrose crystals with boric acid particles.

As to the type of boron compounds, boric anhydride (B203) contains, as the name implies, no molecular water. Tetra boric acid (HzBiOi) contains one-half molecule of water. Meta boric acid (H1302) contains one molecule of water. Ortho boric acid (HaBOs) contains three mole- Theoretically, boric anhydride but this product is diflicult to obtain or manufacture. It is preferable not to use ortho boric acid because of its large content of molecular water. Practically meta boric acid which contains only one molecule of water is the most convenient of the boron compounds. It can be readily produced from ortho boric acid (the usual commercial boric acid) by extracting someof the molecular water contained in the latter. In place of the boron compounds above referred to one may use any non-alkaline material containing B203.

The amount and iineness of the boric acid used has a. bearing upon color formation as well as amount and degree of polymerization. 'I'he reason why a much lighter color product is obtainable with boric acid, used in accordance with the present invention; in comparison with other catalysts used in the production of dextrose vpolymers from molten dextrose, is because with boric acid acting directly on the dextrose crystals, the rate of polymer formation is so rapid that the dextrose does not have time to melt and darken in color. The more thoroughly the ilne boric acid particles coat the dextrose crystals, the more emcient will be the rate of polymerization-and the less colorformation will result. To summarize: color formation is inhibited by (1) flneness of the boric acid powder, the nner the powder the less color; (2) by the' amount of boric acid, namely the more boric acid .of a given ilneness, vthe less color; (8) by a temperature which is below the melting point of the dextrose, in the presence of the catalyst. at least until the polymerization has lbeen initiated; (4) by a relatively short time treatment; and by the absence of water or at least its removal as soon as formed.

Experience has demonstrated that if undried air is circulated through the heating apparatus the polymerizing operation is likely to be detrimentally affected. Generally speaking the lower the atmospheric humidity the better the result. Where there is a substantial amount of moisture in the atmosphere the product is likely to be discolored and contain a substantial, if minor, portion of non-granular, lumpy, fused, poorly polymerized substances which are diflicult to separate, adequately, from the rest of the product either by sifting or by extraction with solvents.

Removal o1'l catalyst from.v ythe dextrose polymer and recovery of boric acid and methanol Referring to the annexed flow sheet, I designates the heating apparatus or polymerizer into which dried crystalline anhydrous dextrose is introduced at 2 and powdered meta boric acid, also preferably pre-dried, is introduced at 3. Dried air is introduced into the polymerizer at 4 and air duced into vessel '8 at 3. Preferably, 25 parts ofv polymer. material is suspended in 125 parts of methanol with mixing produced by the agitator 3 to prevent lump formation which might be caused by thetendency of the polymer particles to adhere to each other. The mixture is then sent through conduit I0 to a vacuum still II.

Distillation o f methanol, and of the methyl 'borate resulting from the reaction between the methanol and boric acid, is'carried on at a temperature between and 15 C. (50 and 59 F.) the distillates going through conduit I2 to tank I3. This continues until 50 parts of the methanol has been distllled off, whereupon 50 parts of fresh i methanol is introduced into the vacuum still II through conduit 8-II. The vacuum distillation is then continued at the same temperature until parts more of the liquid have been distilled off and delivered through conduit I5-i2y tothe tank I3. The material in the vacuum still II is then delivered at Il to a settling tank I1, from which the .major portion. voi? .the liquor is decanted 'through conduit I3-|2 intol the vessel I3, leaving about 15 parts of the liquid mixed with the polymer material. This material is discharged at I3 into'a second vacuum still 2l in which kthe fifteen parts of liquid mixed with the polymer material is distilled off and delivered to vessel I3 Y through' conduit n n. .The 'purified polymer matgrlal is discharged from the vacuum pan at2 f This polymer material may contain 0.25 per cent or less ofprtho boric acid: and its appearance is'practlcaliy identical with the appearance of the original polymer when viewed through the microscope. Y'

I3, as above described. into which is introduced at 23 an alkaline substance in quantity sufncient to neutralize the boric acid. Any suitable neutralizing agent may be used, such as caustic soda, caustic potash or lime. 'I'he caustic soda or caustic potash, for example, neutralizes the boric acid to the corresponding salt, namely, sodium borate or potassium borate, both of which are soluble in methyl alcohol. The neutralized liquid in vessel I3 is then introduced at 24 into a vacuum 51511125. 'from which the methanol is distilled, passing through pipe 26 to the methanol supply line 8, leaving in the vacuum still 25 a powdered residue of alkali borate. The latter is discharged at 21 into a vessel 28 into which is introduced at 29 a mineral acid and water. Suitable mineral acids are hydrochloric acid and sulfuric acid. 'I'he resulting solution consists of boric acid and the corresponding salt, namely sodium or potassium chlorideor sodium or4 potassium sulfate. This solution is introduced at 30 into a concentrating device 3| and the concentrated liquor goes by pipe 32 into a. crystallizer 33 where the boric acid orystallizes as ortho boric acid. The remaining salt solution is discharged from the process at 34. The ortho lboric acid is introduced Lat 35 into a heater 36 into which hot air is introduced at 31 and from which two molecules of molecular water are drawn off at 38, converting th'e material into meta'boric acid, which is conveyed, as indicated at 39, to the meta boric acid supply 3 going to the polymerizer I. f

` One of the principal problems involved. in any system for removing the catalyst and recovering catalyst and removing agent is to prevent the coalescence and adherence one to another of the polymer particles. This result can be obtained: (1) By excluding water from the process as much as possible. (2) By removing the methanol from the polymer as quickly as possible. (3) By using a distillation temperature well below room temperature, for example, 10 to 15 C. (50 to 59 F.)

off. Between this lower limit and the maximum l of 15 C. the lower the temperature the better the results in respect to non-adherence of the polymer particles. (4) By using a. large excess of methanol to prevent. as much as possible, contact between the polymer particles. (5) By the expedient of distilling th'e methanol and methyl borate and replacing the methanol thus removed with fresh methanol. (6) By using a large excess f methanol for the purpose of taking up the molecular water released when boric acid reacts with methanol to form methyl borate.

"Example No. 2.-Two-stage polymerization below and above melting point of dextrose A'uniq'ue feature of the use of boric acid as a catalyst is ,that dextrose can be polymerized by heating to temperatures below the melting point of dextrose, 146 C. (295 F.). Another striking characteristic of this reaction is that if polymerization is started below the melting point of dextrose, the temperature may be raised to a point considerably above the melting point of dextrose and an increased yield of polymers obtained without melting of the material or correspondingly increased coloration. Between 133 and 145 C. (271 and 293 F.) the polymerization reaction is active. Experiments indicate' that if the temperature is then raised slightly above the melting point of dextrose, no melting takes place but, at

' th'ese low' temperatures, there is no substantial increase in the-amount or degreeofpolym'erization. It is necessary to raise the temperature 25 to 30 C., that is, to a temperature of about 175 C. (347 F.) before the polymerization is substantially increased.

The failure of the polymer particles to melt at this high temperature is probably due t the fact that the polymerizing action is initially a surface reaction and the capacity of the dextrose crystals to melt disappears as soon as all of the crystal surfaces have been surrounded with' thin shells or fllms of infusible dextrose polymer.

According to the present example alpha anhydrous dextrose is blended with of meta boric acid after both substances have been preliminarily dried, the meta boric acid being pulverized to 200 mesh, and the mixture heated first for 5 hours at 135 C. (275 F.) and then for 1 hour a 175 C. (347 F.)

The isopropyl alcohol test gives ngures' as indicated in the following table:

Table 2 tfo' mi 0 Isopropyl alcohol added to cc. polymer t gl'nrlzta'd polymer solution to give alcohol precipitated g n mcg; contents oion total dry d it r substance e rose insample un s Percent Comparing these results with those obtained under Example No. 1, it is obvious that both the amount and the degree of polymerization have been increased. The degree of polymerization, in particular, has been increased to avconsiderable extent as indicated by the fact that the percent precipitated withy the addition of cc. of isopropyl alcohol has increased from 35% to 64%. This is more signicantthan the difference under the caption of Degree of polymerization"; since, as stated above, the latter gures represent averages of wide ranges of molecular weights.

It is important to note that in spite of the comparatively high temperature treatment, the resulting product is very light in color, being only slightly darker than the original dextrose'.

Example No. 3.-Meta boric acid and neutral salts as co-catalysts With alpha anhydrous dextrose crystals is blended 5%by weight, of meta boric acid and 1% of nely powdered barium perchlorate. The blend is heated for 5 hours at 140 C. (284 F.) and when analyzed by the isopropyl alcohol test shows results as follows:

Table s Preci itation of isopropyl A scohol contents Tom poly merization m cc. 35 ce. 85 cc.

Per cent Per cent Per cent Per cent 37 29 12 78 perature. Generally'speaking, a salt is considered to be a neutral salt if its water solution has a pH between 5 and 7. Ii' the pH is substantially above 7, the alkalinity of the salt will tend to decompose the dextrose.

Example No. 4.-Meta boric acid and sulfur dios:-

de as the secondari! catalyst Sulfur dioxide can be considered a mineral acid although it is a weak acid in contrast to hydrothe boric acid. In each case the dextrose and the boric acid after treatment will contain hardly more than a trace of the sulfur dioxide. The material is then heated at 140 C. for 5 Vhours while continuing the application of sulfur dioxide to the material under treatment.

'I'he following are the results given by the iso.- propyl alcohol test of the product of this example.

Table 4 Precipitation oi isopropyl alcohol contents Tom poly mcrizstion mec. 36cm Slice.l

Per cent Per' cent Per cent Per cent The sulfur'dioxide may be incorporated with either the dextrose alone or the boric acid alone.

The sulfur dioxide should, of course, be in a dry state.

Eect of impurities in commercial dextrose Experiments have indicated that` for eillcient operation, productive of a large amount and a high degree of polymerization, there must be used with the primary catalyst, boric acid, a secondary or co-catalyst, such as a mineral acid, an acid salt or a neutral salt, the amount of which, however, may be very small, indeed hardly more, in some cases, than a trace. 'Ihis observation does not invalidate the results set forth in Examples 1 and.

2 for the reasons that, first, commercial high purity dextrose always contains a small amount of non-dextrose substance, particularly sodium chloride; and second, these processes were carried out in a starch making plant, the atmosphere in which'contained acidic substances, particularly sulphur dioxide; and under these conditions the primary catalytic action would be to some extent, at least, accelerated by these secondary catalysts. Alpha anhydrous dextrose even -though very close to pure contains, ordinarily, about 0.05% of sodium chloride; and experiments have shown that if commercial alpha anhydrous dextrose be purified by repeated crystallizing operations so as to reduce its ash (sodium chloride) content toa ligure much more closely Vapproaching zero, the amount and degree of polymex-ization, using meta boric acid as a primary catalyst, will be very substantially reduced. Furto drive of:` the hydrate water without melting' the susar. AThe `dehydrated maltose is then thermore. the atmosphere in areas in which industrial and particularly chemical plants such as starch factories are located contains appreciable y amounts of acidic gases, such as sulphur oxides, carbon dioxide, nitrogen oxides and hydrochloric acid, as well as other non-alkaline impurities; and if this air, without, puriiication, is employed, as

in Examples 1 and 2 for removing moisture from appreciably reduced. However, even when the dextrose, the boric acid and also the air`used to eliminate water are all carefully puriiied to remove sodium chloride, acidic substances and other catalytic impurities, some polymerization occurs which indicates that boric acid can be used as a sole catalyst, s

Example No.v 5.-Beta anhydrous dextrose with meta borz'c acdascatalyst reduced to a molten state. However, it has beendiscovered by applicant that beta anhydrous crystals, if in a substantially pure state, that is, free e from the alpha anhydrous, can be successfully polymerized, according to the present invention. Any suitable method may be employed for removing the alpha anhydrous dextrose from commercial beta. Or, if available one may use a beta dextrose having originally a sulciently high beta content. In the pure state the beta will have a melting point of 150 C. (302 F.). `The procedure will then be as follows: r

.To the beta anhydrous dextrose crystals are cooled-*toproom temperature and there is blended therewith-'5% (a trace to 35%) of meta boric added 5%, by weight (a trace to 35%), of meta boric acid pulverized to a 170 mesh or liner, and 0.005% of hydrochloric acid (0.0005 to 0.005).

Table 45 Precipitation at isopropyl alcohol contents oi- Total mhh merization m cc. 35 cc. 85 cc.

:Per cent Per mit Per cent Per cent Example No. Mazte with meta borre acid ana hydrochloric acid as co-catalysts Commercial maltose is in the form or iine crystalline maltose hydrate. 'Ihis sugar is iirst heated for 24 hours at approximately 100 C. (212? F.)

acidfpu-lveriz'edto 170 mesh or iiner and, prefer-- ably, .0g005f`3v hydrochloric acid (0.0005% Ato 0.005%`) "'The blend is heated for 24 hours at C. (212 F.) which is close to the melting I point of maltosemnder normal conditions. The l0' product is a white, powdered maltose polymer, the amount and degree of polymerization, according to the isopropyl alcohol method of analysis, being shown in the following table:`

` ,Tlble 6 Precipitation at isopropyl r alcohol contents oi- Total p0ly K mei-ization 20 cc. 35 cc. 85 cc.

Per cent Per cent Per cent Per cent 4 35 2l 60 25 Example. No. 7.-Maltose withboric acid and hydrochloric acid as co-catalysts and with temperature above melting point of maltose The operating data are the same as in Example No. 6 with the exception that the sugar is ilnally heated to a temperature considerably above the melting point of maltose without, however, affecting the crystal-like Vcharacter or the product. That is, maltose in the form of maltose hydrate crystalsis first heated for 24 hours at approximately 100 C. (212 F.) for the primary purpose of4 driving oil the hydrate water. However, this heat treatment even without the presence of a catalyst initiates polymerization as appears from the fact that after the maltose has been cooled. and there is blended therewith 5% of metaborie acidand 0.005% hydrochloric acid, as in the previous example, the blend may be heated to a temperature of 140 C. (275-284 F.) for 5 hours without any substantial melting of the maltose. The product is a light-colored product of crystallike character, and the amount and degree of polymerization are much increased over the product of Example No. 6, as indicated by the following table:

Table 7 Precipitation at isopropyl alcohol contents of Total non mcrization 20 cc. l 35 cc. 85 cc.

Per cent Per cent Per cent Per om! 46 25 10 8l It will be observedthat the procedures for beta anhydrous dextrose and. for maltose are fundamentally the same as those for alpha anhydrous dextrose. In each case a product is obtained which has the form of the original crystals treated but which consists. of or contains a substantial quantity of the polymerized sugar. This product is, in the preferred processes, light in color being, as in the case of the polymerized alpha anhydrous dextrose, between a light yellowor straw color and white: that is, it is only slightly darker than the sugar treated. There is no, or at least a very small amount of, fused sugar in the product. After the polymerization has been initiated at temperatures below the melting point of the sugar,

larger amounts and degrees of polymerization can be obtained by a heating of the initially polymerized sugar at temperatures considerably above the usual melting points 'of the sugars, without producing any substantial amount of melting. Even in the initial polymerizing operation of the two-stage processes, the temperature may be somewhat higher than the melting point of the sugar if enough-of the primarycatalyst, boric acid, in a, finely enough powdered condition, is used. The amount and degree of polymerization can be increased by the use of a very small amount of a co-catalyst, e. g. an acid, an acid salt or a neutral salt; and in the case of the dextrose, at

- v least a trace of the co-catalyst appears to be v differ from products produced by the polymerization'of molten sugars in that first the form of the product is crystalline, not in the strict crystallographic sense but in the sense that the particles have the form `of the crystals from which the product is obtained. Hence they may ybe referred to as\crystallike particles. These crystals are not dextrose crystals, since to a large extent the dextrose-has been transformed to its polymers. Ihe particles are not crystals ofdextrose polymers which, if crystalline in char- `acten'would have crystal forms, presumably, different from the sugar crystals treated. The particlee do have, however, the form, substantially unchanged of the crystalsfrom which the product is made. And the product, therefore, has all of the advantages, from a 'practical standpoint, of a crystalline product. 'I'he products obtained by the present invention further differ from products produced by the polymerization of molten sugars in that the former contain substantially no reducing sugars and fermentable sugars whereas the latter contain substantial amounts thereof. 'I'he products of the present invention have a dry substance reducing sugar content, calculated as dextrose, of the order of about 0.2%,

Cil

and a content of fermentable sugars of the orderv I of 'about 0.1% by weight. Products produced by the polymerization of sugars in the molten state, on the other hand, have, on-the average, about 10-20% of the reducing value of the original dextross; and it has been found that when hydrogen chloride is used as a catalyst in accordance with the teachings of British Patents 418,481 and 430,- 876, the lowest reducing value obtainable is of the order of about 23%; Similarly, the polymers -resulting from polymerization of dextrose in the molten state contain very substantial quantities of fermentable sugars, as contrasted with the negligible fermentable content of the products of 1 the present invention. Moreover, there is a substantial difference between the products of the present invention and products produced by the polymerization of molten sugars insofar as concerns their hydrolysis by acid. 'I'he former hyg drolyze much more readily than do the latter. The polymerizing operations are essentially anhydrous operations. The aim should be to use, so far as possible, anhydrous materials and to remove as quickly as possible any freed water such as the water which is eliminated from the dextrose as a result of the polymerizing operations.

It will be understood that in the above specific examples the intention has been to set forth the conditions under which the best results are obtainable, to wit, maximum amount and degree of polymerization and minimum color formation. However, it will be possible to operate outside of the speciiled ranges which, generally speaking, are practical and not critical except where so specified, and effect the polymerization of the sugar although not with the best results qualitatively or quantitatively. The invention, therefore, is not to be considered as limited to operations within the specified ranges. It is intended to cover by patent all equivalents in respect to sugars and catalytic materials used, as well as all process modifications within the scope of the hereto'appended claims.

I claim:

l. The process of polymerizing maltose, which comprises heating crystalline maltose in the form of fairly large crystals, under substantially anhydrous conditions, and at a polymerizing tem- Derature which does not reduce the maltose to a molten state, in contact with catalytic material comprising a pulverulent, non-alkaline boron compound containing B203.

2. The process of polymerizing maltose, which comprises heating under substantially anhydrous conditions crystalline maltose in the form of fairly large crystals,` in contact with catalytic material' comprising pulverulent meta boric acid, and at a polymerizing temperature which does not reduce the maltose to a molten state.

3. The process of polymerizing maltose which comprises heating under substantially anhydrous conditions crystalline maltose in the form of fairly large crystals, in contact with a catalytic material comprising a pulverulent, non-alkaline boron compound containing B203, at a polymerizing temperature which does not reduce the maltose to a molten state; and, after polymerization has been initiated, heating the material at a higher temperature below the melting point thereof.

4. The process of polymerizing maltose, which comprises heating under substantially anhydrous conditions maltose in the form of fairly large crystals. at a polymerizing temperature, which does not reduce the maltose to a molten state, in contact with catalytic material comprising a pulverulent, non-alkaline boron compound containing B20: and a small quantity cfa co-catalyst of the group of substances consisting of acids, acid salts and neutral salts.

5. 'I'he process of polymerizing maltose, which comprises blending with crystalline maltose in the form of fairly large crystals, a pulverulent, nonalkaline boron compound containing B203 and also a small amount of a catalyzing substance of the group of substances consisting of acids, acid salts -and neutral salts; and heating the blended material under substantially anhydrous conditions, iirst at a temperature below the melting point of the maltose and then at a polymerizing temperature above the melting point of the maltose but below the melting point of the material resulting from treatment of the maltose at a temperature below the melting point of the maltose.

6. The process of polymerizing maltose, which comprises blending with crystalline substantially anhydrous maltose in the form of fairly large crystals', meta'boric acid and a small amount of sulfur dioxide as a co-catalyst;v -and heating the blend at a polymerizing temperature which does not reduce the maltose to a molten state.

7. 'I'he process of polymerzing'maltose, which comprises blending with crystalline substantially anhydrous maltose inthe form of fairly large crystals meta boric acid in a pulverulent state and a small amount of a secondary catalyst which reduces the polymerizing temperature of the maltose, and which is selected from the group of substances consisting of acids, acid salts and neutral salts; heating the blend at a polymerizing temperature below the'melting point of the maltose to bring about polymerization of the maltose without reducing the material to a molten state; and thereafter heating the material at a substantially increased temperature but below the melting point of said material.

8. The process of polymerizing maltose,. which comprises blending a minimum of about 1%, by weight, of meta boric acid pulverized to a minimum nneness of about 170 mesh, with crystalline substantially anhydrous maltose in the form of fairly large crystals; and heating the blend at a temperature of about 100 C.

9. The process of polymerizing maltose, which comprises blending a minimum of about 1%, by weight, of meta boric acid pulverized to a minimum ilneness of about 170 mesh, with crystalline substantially anhydrous maltose in the form of fairly large crystals; and heating the blend at'a temperature of about C.; and thereafter heating the blend at a temperature o f about C. to C.

10. The process of polymerizing maltose, which comprises blending with crystalline substantially anhydrous maltose in the form of fairly large crystals, meta boric acid and a small quantity of a co-catalyst of the group of substances consisting of acids, acid salts and neutral salts.

11. The process of polymerizing maltose, which comprises blending with crystalline substantially anhydrous maltose in the form of fairly large crystals, meta boric acid and a small amount of hydrochloric acid as a co-catalyst; and heating anhydrous maltose in the form of fairly large crystals, meta boric acid and a small amount of sodium chloride asa co-catalyst; and heating the blend at a polymerizing temperature which does not reduce thel maltose to a molten state.

GERALD JOHN LEUCK. 

